The present invention relates to a data communication method and an apparatus therefor and, more particularly, to the transmission of binary information.
One known transmission technique is the "polar return to zero" scheme. The relationship between binary data to be transmitted and its transmission waveform according to the polar return to zero method is shown in FIG. 1. In this technique, the logical values "1" and "0" of a binary code are represented by using two voltage levels, e.g. +V and -V, respectively, as shown. Each voltage level is always returned to zero for every digit. The signal level changes digit-by-digit, so that timing pulses can be obtained from the data at a receiver. The polar return to zero method, therefore, is known as a self clocking data format. This technique is discussed, for example, in U.S. Pat. No. 3,863,025, particularly in column 1 thereof. Some of its disadvantages are also discussed in the patent. A further disadvantage of this technique is the fact that a relatively broad bandwidth is required for transmission.